In response to 814 requests for indoor environmental quality (IEQ) related health hazard evaluations (HHE) in fiscal year 1993, the National Institute for Occupational Safety and Health (NIOSH) developed a protocol to respond with a single, multievaluation project which was described. The information gathered was entered into a computer database to determine whether common problems occurred. A questionnaire collected information from occupants about work stressors, symptoms, health history, and adverse environmental perceptions. Status and condition information about the heating, ventilation, and air conditioning (HVAC) systems, and serial real time measurements of carbon-dioxide levels, temperature, and relative humidity were collected in the morning and afternoon. NIOSH collected 160 indoor environmental HHEs in 3 months, for sites including schools, office buildings, and healthcare facilities. A report was written for each case with recommendations for improving indoor environments. The majority of problems were related to HVAC design, operation, and maintenance. The findings suggest that lack of maintenance of HVAC systems is in some undefined way related to problems experienced by building occupants, yet in very few cases is a statistically proven relationship found. The authors conclude that it is prudent to optimize comfort and health in the indoor environment.